We present a search for the rare leptonic decays $B^{+}\to e^{+}{\nu }_e$ and $B^{+}\to {\mu }^{+}{\nu }_{\mu }$, using the full $\mathrm{\Upsilon }(4S)$ data sample of $772\times 10^6$ $B\overline{B}$ pairs collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. One of the $B$ mesons from the $\mathrm{\Upsilon }(4S)\to B\overline{B}$ decay is fully reconstructed in a hadronic mode, while the recoiling side is analyzed for the signal decay. We find no evidence of a signal in any of the decay modes. Upper limits of the corresponding branching fractions are determined as $\mathcal{B}(B^{+}\to e^{+}{\nu }_e)<3.5\times 10^{-6}$ and $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu })<2.7\times 10^{-6}$ at 90% confidence level.

• Received 25 June 2014

DOI:https://doi.org/10.1103/PhysRevD.91.052016